A friction drive system for accurate positioning

A transmission system for positioning a conventional moving table has been constructed. The gearbox which has been inserted between the lead screw and the driving stepping motor is of the friction type. The resolution of the system has been measured to be less than 0.01 μm     

Lateral hypothalamic syndrome in rats: a comparison of the behavioral and neurochemical effects of lesions placed in the lateral hypothalamus and nigrostriatal bundle

The effects of total (T-NSB) and subtotal (S-NSB) destruction of the nigrostriatal bundle were compared with the effects of large lateral hypothalamic (LH) lesions on various aspects of the lateral hypothalamic syndrome. The T-NSB and LH lesions produced equivalent decreases in caudate and telencephalic contents of dopamine and norepinephrine, while with the exception of telencephalic dopamine, S-NSB lesions had consistently smaller effect. The T-NSB and LH lesions produced equivalent effects on duration of aphagia and adipsia (Stages 1 to 3) and on long-term decreases in body weight and ad lib water consumption, and these effects were always greater than those produced by the S-NSB lesion. These aspects of the lateral hypothalamic syndrome appeared to be related to the interruption of the nigrostriatal bundle and consequent decrease in caudate dopamine. The T-NSB and S-NSB lesions produced equivalent long-term deficits in water regulation as measured by drinking in the absence of food or in response to intra- and extracellular dehydration, but these deficits were always significantly less than those produced by the LH lesion. It was concluded that these regulatory deficits were not related to destruction of catecholamine pathways. All three lesions totally blocked eating in response to a glucoprivic challenge. This aspect of the lateral hypothalamic syndrome, therefore, results from destruction of a small portion of the lateral diencephalon and may be related to the interruption of the dopaminergic mesolimbic system.     

Ni53Mn22Ga25磁性形状记忆合金的相变内耗

研究了Ni53Mn22Ga25磁性记忆合金在190～390K温度范围的内耗行为。结果表明．当合金发生正、逆马氏体相变时出现明显的内耗峰,并伴随模量变化出现极小值。马氏体相变后继续降温。在215K附近出现新的内耗峰,模量明显增高。合金在居里温度发生顺磁及铁磁正反转变时．内耗及模量均不发生变化。对上述现象进行了分析和讨论。     

The validity and reliability of a portable slip meter for determining floor slipperiness during simulated heel strike

A previously developed test rig was used as starting point for designing a portable slip meter with two new features. First, an inflatable pneumatic test wheel, consisting of six slider units, was introduced as the impacting contact element relative to floor surface. Second, an inductive trigger was built into the system to facilitate a precise timing of the slider-floor contact during the test. This new test rig was designed to measure transitional friction properties of contaminated floor surfaces during simulated heel strike, which is considered the most critical phase of gait from the slip and fall point of view. Another objective was to quantify the validity and reliability of this test method in the laboratory, but not yet in the field. The measurement process was evaluated on eight wet and oily floor surfaces (vinyl and ceramic tile floorings) using two slider materials (plain, profiled), two normal loads (100, 200 N), and two sliding velocities (0.15, 0.30 m/s) as independent variables. The outputs of the portable slip meter, in terms of transitional friction coefficients, were compared to force platform-based friction values and to slip resistance values obtained with a slip simulator apparatus for laboratory testing of shoes and floor surfaces. The outputs were also evaluated against slipperiness ratings made by three male subjects in paired comparison trials, in which the subjects walked over eight wet floor surfaces wearing shoes with the plain soling material. The results showed that test option 200 N and 0.15m/s led to optimum validity despite its tendency to promote frictional vibrations (stick-slip) in the contact surface. Compared to the lower sliding speed, the higher speed reduced both stick-slip and measurement bias. Test option 200 N and 0.30 m/s was the most reliable one in this experiment. It yielded lower friction coefficients than any other test option and reduced the likelihood of underestimating slip and fall hazards. The results implied that the minimum friction coefficient was 0.25 for preventing a fall on wet floor surfaces, whereas the limit for preventing a slip was in the range 0.30-0.35. Transitional friction measurement was found to be a valid and reliable indicator for slip resistance. A more accurate control of the normal force during testing is needed for actual field use of the test method.     

分支水平井完井设计与实践

在介绍分支井完井TAML分级情况及完井设计原则的基础上。详细介绍了塑性水泥固井技术在两口分支水平井中的应用情况,以梁46-支平1井为例,分析了分支井完井应注意的问题,对进一步推广应用分支井技术及提高分支井固井质量具有重要意义。     

The Frictional Properties of Thin Inorganic Halide Films on Iron Measured in Ultrahigh Vacuum

Friction coefficients are measured in ultrahigh vacuum using a tungsten carbide tribopin against thin films of sodium chloride and potassium iodide deposited onto clean iron. It is found, in accordance with previous measurements for potassium chloride on iron, that the friction coefficient falls from an initial value of 2 for the clean iron surface to a minimum value after a few tens of Ångstroms of the halide have been deposited onto the surface, and remains constant for thicker films. The minimum friction coefficient is independent of applied load and therefore obeys Amontons' law. Simple theories for the effect of a low-shear-strength film suggest that the friction coefficient should depend on the shear strength of the film. This idea is tested by plotting the minimum friction coefficient versus the hardness of the film material, which is proportional to its shear strength, where a linear correlation was found. The lack of dependence of friction coefficient with film thickness for thicker films implies that ploughing forces do not contribute significantly to the friction coefficient.     

Effect of Copper Content on the Mechanical and Tribological Properties of ZnAl27-Based Alloys

One binary ZnAl27- and five ZnAl27-based ternary alloys containing 1–5% Cu were produced by permanent mould casting. Their friction and wear properties were examined using a block-on-ring test machine after determining their hardness and tensile strength. It was observed that the hardness and tensile strength of the ZnAl27-based ternary alloys increased with increasing copper content up to 2% due to solid-solution hardening, above which their tensile strength decreased, while hardness continued to increase. This is attributed to the formation of copper-rich and T phases, which reduce the solid-solution hardening of the alloys. It was found that the wear volume loss of the ZnAl27-based alloys decreased with increasing copper content up to 2% but showed a small increase above this level. Therefore, it was concluded that the wear resistance of ZnAl27-based alloys containing 1 to 5% Cu correlates well with their tensile strength. In addition, smearing and scratches were found to be the main features of the wear surfaces of the ZnAl27-based alloys under static loading and lubricated sliding conditions.     

Effective Thermal Conductivity and Permeability of Aluminum Foam Materials1

An experimental measurement program was performed to determine thermophysical properties of aluminum-based foam metals. The effective thermal conductivity k _e and permeability K were investigated in detail. Experimental facilities were fabricated, and the measurement procedures and methodologies were evaluated. One-dimensional heat conduction was considered to determine k _e . The results indicate that k _e increases as the porosity decreases. However, no noticeable changes in k _e were detected from variations of the cell size of the foam metal at a fixed porosity . The permeability K is substantially affected by both and the cell size. An empirical correlation for the friction factor f is proposed based on the concepts of K and inertial effect.     

磁浮列车用铜基受电靴滑块材料的研究

研究了一种新型Cu-Sn-Pb-Cr-C受电靴滑块材料,并进行了性能测定和组织观察.结果表明:受电靴滑块材料具有优良的综合性能,其抗拉强度为138.1MPa,断口局部范围内有韧断特征;摩擦系数为0.38,其摩擦性能大大优于纯Cu;材料的电导率可达74%IACS,明显高于纯Al(60%IACS).从其微观结构可以发现,试样材料中Cu基体以连续网状形式分布,加入的石墨比较均匀地分布在网络空隙内,充分发挥了材料的导电性能及石墨的自润滑性能.     

钢纤维对摩擦材料性能的影响

树脂基复合材料性能优异,被大量用做汽车制动材料.以酚醛树脂为基体,钢纤维为增强纤维,添加填料,采用热压法制成刹车片,并进行摩擦试验.通过试验研究了酚醛树脂基复合材料中钢纤维不同添加量(质量分数)对复合材料冲击强度、摩擦性能的影响.结果表明:该配方类型中,在100～300℃温度范围内,材料冲击强度先增大后减小,钢纤维质量分数为24%时为转折点;材料的摩擦系数先增大后减小,钢纤维质量分数为26%时为转折点;磨损率随钢纤维添加量的增加而增大,钢纤维最佳添加量为24%～26%.